Temperature sensor and related method

Abstract

A temperature sensor, including a conduction path, between a line at a supply voltage and a common ground terminal of the temperature sensor, including a capacitor, a resistor and a reverse biased diode a junction temperature of which is to be sensed; a digital circuit coupled with the capacitor, the resistor and the diode, configured to compare a charge voltage of the capacitor with an upper threshold voltage and with a lower threshold voltage, and to generate in operation an output sense signal that switches to a first logic level when the charge voltage attains the lower threshold voltage and to a second logic level when the charge voltage attains the upper threshold voltage, the digital circuit being configured to connect the resistor electrically in parallel with the capacitor to discharge the capacitor when the output sense signal is at the second logic level, and to connect the capacitor so as to be charged by a reverse saturation current flowing throughout the reverse biased diode when the output sense signal is at the first logic level.

What is claimed is: 
     
       1. A temperature sensor, comprising:
 a conduction path between a line at a supply voltage and a common ground terminal of the temperature sensor and including a series connected capacitor, resistor and a plurality of reverse biased diodes coupled in parallel and being physically proximate each other, a junction temperature of the plurality of reverse biased diodes being sensed; and 
 a digital circuit coupled with said capacitor, said resistor and said plurality of reverse biased diodes, the digital circuit configured to compare a charge voltage of said capacitor with an upper threshold voltage and with a lower threshold voltage, and to generate in operation an output sense signal that switches to a first logic level when said charge voltage attains said lower threshold voltage and to a second logic level when said charge voltage attains said upper threshold voltage, said digital circuit being configured to connect said resistor electrically in parallel with said capacitor to discharge said capacitor when said output sense signal is at said second logic level, and to connect said capacitor so as to be charged by reverse saturation currents flowing through said plurality of reverse biased diodes when said output sense signal is at said first logic level. 
 
     
     
       2. The temperature sensor of  claim 1 , wherein said digital circuit comprises:
 a comparator with hysteresis configured to receive as input the charge voltage of said capacitor, to compare the charge voltage with an upper threshold voltage and with a lower threshold voltage, and to generate in operation an output sense signal that switches to a first logic level when said charge voltage attains said lower threshold voltage, and to a second logic level when said charge voltage attains said upper threshold voltage; and 
 a controlled switch configured to connect said resistor electrically in parallel with said capacitor when said output sense signal is at said second logic level, and to connect said capacitor so as to be charged by a reverse saturation current flowing throughout said reverse biased diode when said output sense signal is at said first logic level. 
 
     
     
       3. The temperature sensor of  claim 1 , wherein said reverse biased diode is a Schottky diode. 
     
     
       4. The temperature sensor of  claim 1 , wherein said lower threshold voltage is one third of said supply voltage and said upper threshold voltage is two thirds of said supply voltage. 
     
     
       5. The temperature sensor of  claim 1 , wherein said first logic level is high and said second logic level is low. 
     
     
       6. The temperature sensor of  claim 1 , wherein said digital circuit is a 555 timer IC configured as an astable circuit. 
     
     
       7. The temperature sensor of  claim 1 , wherein the digital circuit further comprises a hysteresis comparator. 
     
     
       8. The temperature sensor of  claim 1 , further comprising a timer circuit configured to convert temperature information to a digital signal. 
     
     
       9. A wearable apparatus for monitoring the health state of a patient, comprising:
 a temperature sensor including a conduction path between a line at a supply voltage and a common ground terminal of the temperature sensor, the conduction path including a capacitor, a resistor and a plurality of parallel-connected reverse biased diodes, connected in series between the line at the supply voltage and the common ground terminal, wherein a reverse saturation current through each of the plurality of parallel-connected reverse biased diodes is function of a junction temperature of the diode and wherein each of the plurality of parallel-connected reverse biased diodes is positioned relative to the other ones of the plurality of parallel-connected reverse biased diodes so the junction temperatures of all the plurality of parallel-connected reverse biased diodes are approximately equal; 
 a digital circuit coupled with said capacitor, said resistor and said plurality of parallel-connected reverse biased diodes, the digital circuit configured to compare a charge voltage of said capacitor with an upper threshold voltage and with a lower threshold voltage, and to generate an output sense signal that switches to a first logic level when said charge voltage attains said lower threshold voltage and to a second logic level when said charge voltage attains said upper threshold voltage, said digital circuit being configured to connect said resistor electrically in parallel with said capacitor so that substantially no reverse saturation currents flowing through said plurality of parallel-connected reverse biased diodes flows to said capacitor, and configured to discharge said capacitor through the resistor when said output sense signal is at said second logic level and to connect said capacitor so as to be charged by the reverse saturation current flowing throughout said reverse biased diode when said output sense signal is at said first logic level, 
 wherein said reverse biased diode is embedded in said apparatus such to be in contact with the skin of the patient when the apparatus is worn. 
 
     
     
       10. The wearable apparatus of  claim 9 , wherein the digital circuit further comprises a hysteresis comparator. 
     
     
       11. The wearable apparatus of  claim 9 , further comprising a timer circuit configured to convert temperature information to a digital signal. 
     
     
       12. A method of generating an output sense signal representative of a junction temperature of a reverse biased diode, comprising:
 providing a plurality of reverse biased diodes coupled in parallel and positioned proximate one another to approximately equalize junction temperatures of the plurality of reverse biased diodes; 
 providing a conduction path between a line at a supply voltage and a common ground terminal, the conduction path including the plurality of reverse biased, a capacitor, and a resistor, coupled in series in that order between the line at the supply voltage and the common ground terminal; 
 comparing a charge voltage of said capacitor with an upper threshold voltage and with a lower threshold voltage; 
 generating said output sense signal that switches to a first logic level responsive to said charge voltage attaining said lower threshold voltage and to a second logic level responsive to said charge voltage attaining said upper threshold voltage; 
 coupling said resistor electrically in parallel with said capacitor by coupling a node defined at the interconnection of the plurality of reverse biased diodes and the resistor to the common ground terminal to discharge said capacitor when said output sense signal is at said second logic level, and 
 coupling said capacitor so as to be charged by total reverse saturation current equal to the sum of respective reverse saturation currents flowing through the plurality of reverse biased diodes when said output sense signal is at said first logic level by isolating the node defined at the interconnection of the reverse biased diode and the resistor from the common ground terminal. 
 
     
     
       13. The method of  claim 12 , wherein the comparing is done using a hysteresis comparator. 
     
     
       14. The method of  claim 12 , further comprising converting temperature information to a digital signal using a timer circuit. 
     
     
       15. The method of  claim 12 , wherein coupling the node defined at the interconnection of the reverse biased diode and the resistor to the common ground terminal comprises closing a switch coupled between the node and the common ground terminal. 
     
     
       16. The method of  claim 15 , wherein isolating the node defined at the interconnection of the reverse biased diode and the resistor from the common ground terminal comprises opening the switch.